Field of the Invention
The invention relates to a method for magnetic resonance imaging, and a magnetic resonance apparatus and a non-transitory data storage medium for implementing such a method
Description of the Prior Art
In a magnetic resonance device, also called a magnetic resonance tomography system, the body to be examined of an object to be examined, for example a patient, a healthy training volunteer or a phantom, is exposed to a relatively high basic magnetic field with the use of a basic field magnet, for example 1.5 or 3 or 7 tesla. In addition, gradient pulses are activated with the use of a gradient coil arrangement. A radio-frequency antenna arrangement emits radio-frequency pulses, for example excitation pulses, from suitable antennas that cause the nuclear spins of specific atoms excited to resonance by these radio-frequency pulses to be tilted by a defined flip angle relative to the magnetic field lines of the basic magnetic field. Upon relaxation of the nuclear spins, radio-frequency signals, known as magnetic resonance signals, are emitted, received by suitable radio-frequency antennas and then processed further. Finally, the desired image data can be reconstructed from the raw data acquired in this manner.
Therefore, for a specific scan, a specific magnetic resonance sequence, also referred to as a pulse sequence, is to be emitted, this sequence being composed of a series of radio-frequency pulses, for example excitation pulses and refocusing pulses and gradient pulses, which are to be emitted with suitable time coordination in different gradient axes along different spatial directions. Chronologically coordinated therewith, readout windows are set, which predetermine the periods of time in which the induced magnetic resonance signals are acquired.
Physiological parameters of the object to be examined, for example respiratory motion or cardiac motion of the object to be examined, can influence magnetic resonance scan data acquired during the magnetic resonance imaging. The physiological parameters of the object to be examined can result in an unwanted change in the magnetic resonance scan data acquired during the magnetic resonance imaging, for example they can influence a signal intensity and/or a phase of the acquired magnetic resonance scan data. This influence can for example occur as a result of motion-induced susceptibility changes. Particularly with echo-planar imaging, the influence of the physiological parameters of the object to be examined can be especially strongly distinct. Also conceivable is the occurrence of motion artifacts in the acquired magnetic resonance image data.
Different methods are known that at least partially compensate of the physiological parameters of the object to be examined during the magnetic resonance imaging. One known possibility for such compensation is the use of navigators during the magnetic resonance imaging. In a navigator scan, the acquisition of the navigators typically includes the activation of radio-frequency pulses and the read-out of navigator slices in addition to the sequence elements used by the magnetic resonance sequence to record the diagnostic magnetic resonance scan data. In this context, the navigator slices are typically only used to compensate the physiological parameters, and can be discarded after the completion of the magnetic resonance sequence.